Patent GB-867206-A (GB)
Title: The production of polarising elements incorporating glass flakes
IPC: G02B5/30
Filed: 1957-07-01
Abstract: A polarizing sheet material comprises a synthetic resin binder with glass flakes distributed therein and a further substance interposed between part of the contiguous surfaces of the glass flakes and the synthetic resin, this substance having a refractive index differing by at least 0,2 from that of the glass and the synthetic resin.  The substance may be titania or zirconia and forms a high index coating on the glass flakes as by mixing in a drum tumbler.  Alternatively, a high index coating may be formed by treating the glass flakes with titanium tetrachloride and ammonium hydroxide and pyrolizing at about 600 DEG F.; by exposing heated glass flakes to a gaseous atmosphere of tetraisopropyl titanate; or by dissolving tetraisopropyl titanate in a solvent and forming a titanium silicate coating by heating. Such a coating may be formed during the manufacture of the glass flakes (see Group XXIII).  Preferably, the substance disposed between the glass flakes and the synthetic resin binder is a gas and several methods of forming gases within the sheet material are described. Thus, the flakes may be mixed with an amount of binder equal to 1-5% of the total weight of glass and binder so that the flakes are only partially wetted and on curing the sheet gaseous spaces are formed. Alternatively, the binder dissolved in a solvent may be applied to the flakes and the mix heated to evaporate the solvent.  Gas under pressure may also be applied to a slurry of flakes and binder in a closed mixer.  A cured sheet consisting of glass flakes and synthetic resin binder may be converted into a polarizer by subjecting it to mechanical or thermal shock or to high frequency electromagnetic waves.  Again, before adding the binder, glass flakes mixed with monomeric styrene may be heated under vacuum to eliminate some of the entrapped air or all of the entrapped air, in the latter case a controlled amount of air being reintroduced.  Polarizing elements may also be formed by curing a sheet of flakes and binder at a temperature above the maximum curing temperature to cause rapid or overcuring of the binder.  Before mixing flakes with the binder, they may be given a non-adhesive surface by treatment with silicone or organic wax or they may be moistened as with water.  A gassing agent, such as styrene or peroxide, may be mixed with the resin binder.  An ordinary glass flake sheet may be attached to the surface of the cured sheet or positioned between the heated platen and the curing resin so that it will adhere to the cured sheet and form a support. The polarizing elements may also be extruded as rods or tubes.  The synthetic resin binder may be polyvinyl acetate, polyvinyl pyrrolidone, polymethyl methacrylate, polystyrene or a polyester.ALSO:Light polarising sheet material is obtained by dispersing glass flakes in a synthetic resin binder and forming spaces between the glass flakes and resin filled with a gas.  The flakes may be mixed with 1-5% by weight of binder so that the flakes are only partially wetted.  On curing gaseous spaces are formed. Binder dissolved in a solvent may be applied to the flakes and the mix heated to evaporate the solvent.  Gas under pressure may be applied to a slurry of flakes and binder in a closed mixer.  Glass flakes mixed with styrene may be heated under vacuum to remove entrapped air, a controlled amount of air introduced, the material mixed with a compatible binder and secured.  Glass flakes and binder may be heated above normal curing temperatures to partially decompose the binder.  The flakes may be rendered non-adhesive before applying the binder.  A gassing agent may be present in the binder.  The binder may be polyvinyl acetate, polyvinylpyrrolidone, polymethyl methacrylate, polystyrene or a polyester.